A platform is the set of elements and interfaces that are common to a family of products. We have previously presented a method for designing product families based on platforms that quantifies performance and cost metrics. That approach allows a team of engineers to design and evaluate candidate platforms, given perfect understanding of the designs and requirements. In this paper we present a model to account for uncertainty present during the development of those product families. Real options concepts are introduced to model the risks and delayed decision benefits present under uncertainty in technologies, funding, etc. We develop a quantitative measure of the value to the company for different family designs, and apply it to select the most appropriate design from the possible alternatives. An application to the design of platform-based families of spacecraft is shown. Results from the models indicated the platforms that were most valuable to the company under different scenarios, as well as the sensitivity of the value of each design to different uncertainty factors.